The present invention relates to a process and an apparatus for artificial ventilation for assisting the volumetric inspiration of a patient.
Modern respirators such as, for example, the one described in United Kingdom Patent No. 2,054,387, employ modes of ventilation in which a patient breathes intermittently or continuously in a spontaneous manner. With such apparatus, when the patient inspires spontaneously in the circuit of the apparatus, a device detects the drop in pressure appearing at the beginning of inspiration, or "suction", and provokes a rise in pressure of the circuit to a level higher by some millibars than the initial level. This aids in the transfer of the gas insufflated towards the lungs. This level of pressure is predetermined by the prescriber or prescribing physician of the ventilation. When the patient has received a volume of gas such that the rise in the intrapulmonary pressure is equal to the rise in the pressure of the circuit, the resistance that the patient then opposes against the flow rate of gas interrupts the phase of inspiration. By control of the flow rate, the patient is thus ensured a flow rate of inspiration gas corresponding to a balanced pressure or positive end of expiration pressure, hereinafter designated "PEEP", by detecting the drop in pressure of the flow of gas towards the patient caused by the inspiration and by increasing the flow rate of this gas flow proportionally to the drop in pressure detected with respect to balanced pressure PEEP.
The apparatus carrying out such a process comprises a source of supply of pressurized gas, an inspiration tube connected to the patient, a demand valve connected between the source of supply and the inspiration tube. The demand valve which constitutes means for controlling the flow rate of gas distributed towards the patient as it comprises a reference chamber connected to an expiration tube connected to the patient and to the output of a Venturi tube communicating by its inlet to a supply tube connecting it to the source of supply of gas in order to control the demand valve so that it sends the gas to the patient at the balanced pressure or positive end of expiration pressure PEEP.
The interest of such a process is obvious for a patient whose breathing is insufficient, since it is demonstrated that, from the hemodynamic standpoint, a predetermined spontaneous ventilation is preferable to a controlled ventilation in intermittent positive pressure, because the intrapulmonary pressure obtained in the first case is notably lower than in the second. However, this technique presents a considerable drawback, namely that aided inspiration induces comfort in the patient who is then not incited to make an effort. Such a situation consequently renders withdrawal difficult and leads to the necessity of making frequent adjustments of the threshold of assistance pressure.
Another patent, United Kingdom Patent No. 1,237,273, owned by Blease Medical Equipment Limited, the inventor of which is Roger Edward Wentworth Manley, was brought to the inventor's attention, which shows a single air source and a bellows. However, the bellows is not used in the inhalation circuit.